This application generally relates to the field of marine geophysical prospecting. More specifically, the application relates to equipment and methods for geophysical prospecting. In particular, anti-debris equipment and methods are disclosed.
In the oil and gas exploration industry, marine geophysical prospecting is commonly used in the search for subterranean formations. Marine geophysical prospecting techniques yield knowledge of the subsurface structure of the Earth, which is useful for finding and extracting hydrocarbon deposits such as oil and natural gas. Seismic surveying and electromagnetic surveying are two of the well-known techniques of marine geophysical prospecting.
For example, in a seismic survey conducted in a marine environment (which may include saltwater, freshwater, and/or brackish water environments), one or more seismic energy sources are typically configured to be submerged and towed by a survey vessel. The survey vessel is typically also configured to tow one or more (typically a plurality of) laterally-spaced streamers through the water. Electromagnetic surveys may tow equipment, including streamers, in a similar fashion. Some techniques of geophysical prospecting involve the simultaneous use of seismic and electromagnetic survey equipment.
In a typical marine survey, the streamers on which the sensors are located are very long, typically multiple kilometers in length. Some surveys may be conducted with a single streamer, while some surveys utilize multiple streamer systems including one or more arrays of streamers. The exterior of towed equipment, such as streamers and related equipment, are subject to accumulation of debris (e.g., seaweed, marine organisms, barnacles, or algae). Such accumulations can increase drag on the equipment as it is towed through the water, making towing more difficult and expensive, and subjecting the equipment to malfunction or damage, as well as causing turbulence that may increase towing noise and degrade the quality of recorded signals.
Scrapers may be employed to remove debris from the exterior of marine survey equipment, such as streamers. A common type of scrapers is a metal scraper (e.g., barnacle scraper) that may be clamped around a streamer. Some scrapers may have a tendency to slide over the debris without removing it. Some scrapers may also have a tendency to be clogged by debris. As a result, the cleaning operation may need to be suspended to unclog the scraper. Inefficiency in the cleaning operation typically increases survey downtime and survey cost. Such cleaning operation can be difficult to perform, dangerous to personnel in the event of unexpected rough water, and, depending on the skill of the cleaning operator, may risk damage to the streamer.
Geophysical equipment including some streamers known in the art may include sensors, streamer positioning devices, birds, connectors, and various other devices along their lengths. Geophysical equipment may include, for example, streamer positioning devices (e.g., lateral force and depth control devices known as “birds”) and sensors for acoustic detection. Moreover, streamers known in the art may have sections along their length with different diameters (either by design or as a result of towing effects). There exists a need for a marine geophysical equipment cleaning device that can traverse an entire deployed streamer, wherein the streamer has a varying diameter along the length, and/or the streamer includes such components as sensors, streamer positioning devices, birds, connectors, and other devices.
While at least a portion of the explanation of the need provided herein refers to seismic surveying, it is important to recognize that the survey system here is not limited to seismic survey but rather any survey system which includes a cable towed by a vessel including a survey vessel. Such other types of cables may include, without limitation, electrodes, magnetometers and temperature sensors. Accordingly, the references to seismic streamers are provided as non-limiting examples.